Nanotips are widely used in various fields including nano-device measurement and characterization, scanning tunneling microscopy, conductive atomic force microscope (AFM), nanofabrication, nanolithography, biosensing, etc. Nanotips can be made from conductive materials such as tungsten, highly doped silicon, and precious metals. Alternatively, a nanotip may be composed of a non-conductive body coated with one or more layers of conductive materials. Due to its robustness and high density, its characteristic of being amenable to chemical etching, tunable tip geometric shape, highest melting point of all the non-alloyed metals, and relatively good oxidation resistance in air, tungsten (W) nanotip is one of the most favored conductive nanotips. Typically, nanotip apex sharpness and geometric shape requirements vary depending on the specific context in which a nanotip is applied. The sharpness of a nanotip is measured by the radius of curvature (ROC) at the apex, also known as apex radius. In general, the sharper the nanotip apex is, the smaller the ROC. The apex radius of commercially available nanotips ranges typically from about 50 to 70 nm.
Nanoprobing is a valuable tool for electrical failure analysis (FA) in current FA metrology for fault isolation. A nanoprobing system typically includes a scanning electron microscopy (SEM) or an AFM integrated with four to eight nanomanipulators with nanotips, which are connected to a parametric analyzer. Such a system is capable of direct transistor characterization at the contact level. Yet, the minimum device size tends to decrease with further progression in transistor scaling. This requires nanotips with sufficiently small ROC to serve as probes in a nanoprobing system. Currently, no commercially available nanotips can be used for probing, for example, 14 nm and 10 nm technology node devices.
Various tip sharpening methodologies have been developed with different technologies including field emission deposition, oxidation in oxygen environment or high electrical field in air, chemical reverse etching, etc. However, these methodologies require complicated or expensive setups and suffer from poor repeatability and low yield.
Accordingly, there remains a need to develop a low-cost method for fabricating sharp nanotips.